Spontaneous lorentz breaking and massive gravity

Theories with an extra spin-two field coupled to gravity admit a massive phase with broken Lorentz symmetry. While the equivalence principle is respected, the Newtonian potentials are in general modified, but they may be protected by a scale symmetry of the coupling term. The gravitational waves phenomenology is quite rich: two gravitons, one massive and one massless, oscillate and propagate with distinct velocities, different from the speed of light. A time of flight difference between gravitons and photons from a common source would provide a clear signal of this theory.     

On the deconstruction of time

In this note we discuss the possibility of getting a time rather than space in the scenario of (de)construction of a new dimension.     

Neutron-mirror-neutron oscillations: how fast might they be?

We discuss the phenomenological implications of the neutron (n) oscillation into the mirror neutron (n'), a hypothetical particle exactly degenerate in mass with the neutron but sterile to normal matter. We show that the present experimental data allow a maximal n-n' oscillation in vacuum with a characteristic time tau much shorter than the neutron lifetime, in fact as small as 1 sec. This phenomenon may manifest in neutron disappearance and regeneration experiments perfectly accessible to present experimental capabilities and may also have interesting astrophysical consequences, in particular, for the propagation of ultra high energy cosmic rays.     

Double protection of the Higgs potential in a supersymmetric little Higgs model

A mechanism of double protection of the Higgs potential, by supersymmetry and by a global symmetry, is investigated in a class of supersymmetric models with the SU(3)cxSU(3)wxU(1)x gauge symmetry. The electroweak symmetry can be then broken with no fine-tuning at all.     

Self-guiding electromagnetic beams in relativistic electron–positron plasmas

Nonlinear interaction of an intense electromagnetic (EM) beam with relativistically hot electron–positron plasma is investigated by invoking the variational principle and numerical simulation, resting on the model of generalized nonlinear Schrödinger equation with saturating nonlinearity. The present analysis shows the dynamical properties including the possibilities of trapping and wave-breaking of EM beams. These properties of EM beams may give a significant clue for the gamma-ray burst.     

Dark matter and generation of galactic magnetic fields

We look for possible spectral features and systematic effects in the Fermi LAT publicly available high-energy gamma-ray data by studying photons from the Galactic center, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and from the Earth limb. Apart from the already known 130 GeV gamma-ray excesses from the first two sources, we find no statistically significant excesses from any of the cosmological sources nor from any control region. Therefore our main effort goes to the study of gamma rays appearing from the Earth limb. In the energy range of 30 to 200 GeV the Earth limb gamma-ray spectrum follows a power-law with spectral index 2.86±0.05 at 95 % CL, in a good agreement with the PAMELA measurement of the cosmic ray proton spectral index of 2.82–2.85, confirming the physical origin of the limb gamma-rays. In subsets of the Earth limb data at small photon incidence angle spectral features occur, including a feature at 130 GeV. We observe a systematic ～2σ-level difference in the Earth limb spectra with small and large incidence angles. The behavior of those spectral features as well as the background indicates that those may be statistical fluctuations or complicated unknown systematic effects of the Fermi LAT. In the latter case, only the Fermi LAT Collaboration can give the final answer having access to raw data and all details of the reconstruction.